Quoting Commentary for I Samuel 4:18

A Midrashic approach to the words: “it was on the eighth day” (based on Tanchuma Shemini 2) David says in Psalms 75,5: אמרתי להוללים אל תהולו, “I said to the frivolous men: ‘do not be frivolous!’” Instead of reading אל תהולו, read אל תחולו, “do not break out in dance.” The reason is that true joy does not linger with man in this world but only in the world to come. Many people who rejoice and are happy today may find that on the morrow they have no such cause for happiness and exuberance. This is why Solomon, [using the same expression as David, מהולל, Ed.] said: (Kohelet 2,2) לשחוק אמרתי מהולל, “of revelry I said: ‘it is mad!’” If you require proof of the truth of both statements take a look at what happened at the creation. When G’d completed His handiwork at the end of 6 days and He reviewed it (Genesis 1,31) He was very pleased as we know from Psalms 104,31: “may the glory of the Lord endure forever, may the Lord rejoice in His works!” In the verse from Genesis we are told that “G’d looked at His entire handiwork and behold, it was very good!” Only a few chapters later (Genesis 6,6) the Torah reports וינחם ה' כי עשה את האדם בארץ ויתעצב אל לבו, “Hashem had to comfort Himself that He had made man on earth, and it caused Him sadness in His heart.” Keeping this verse in mind, Assaph said in Psalms 75,5 not to indulge in frivolous merriment. If even G’d’s joy did not endure, how much less is the chance that man’s joy on earth will endure!
Avraham progressed in his life and became exceedingly great and wealthy killing the most powerful kings on earth in the process. In his old age G’d gave him a son from Sarah. His joy was unbounded. A few years later G’d commanded him to take his son and to offer him up as a sacrifice. Even after having mastered that trial and being commended by G’d (Genesis 22,16-17), he went back from Moriah and had to bury his beloved wife Sarah. His joy had been short-lived. He even had trouble being given a suitable plot where to bury Sarah. In the end, he was literally fleeced, having to pay an astronomical sum of 400 shekel for a hole in the ground.
Yitzchak who enjoyed phenomenal success in Gerar, seeing his investment returned one hundred-fold, (Genesis 26,12) faced expulsion shortly thereafter as the Philistines became jealous of his wealth. His joy had been very short-lived. After Avimelech realized that he had wronged him and apologized and made a treaty with him (Genesis 26,28) and he surely thought that “he had it made,” we read that his eyesight failed him and that he almost made a fatal error bestowing the blessing on a son whom he had considered worthy but who in the event had been unworthy all along. His joy had proven to be short-lived. If a Yitzchak who had been a living example of what it means to be a “total-offering, i.e. burnt-offering,” was not allowed permanent joy on earth, i.e. the fruits of his total dedication to G’d’s command, how much less may we ordinary mortals expect joy on earth to be enduring.
Yaakov experienced great joy when he had the dream with the ladder, seeing angels ascending and descending, a promise from G’d that He would be with him, etc. (Genesis 28, 12-13). Not long afterwards he experienced a whole string of misfortunes, beginning with being tricked out of his chosen wife Rachel, the rape of Dinah, and concluding with the disappearance of Joseph. If Yaakov the righteous, of whom G’d had said that He would boast of such a man (Isaiah 49,3), could not hold on to his joy in this life, what can we lesser individuals expect in the way of enduring joy on earth?
Joshua experienced great joy in his time, he settled the Jewish people on their land, killed 31 Kings, was promised by G’d that no one would rise against him successfully, and enjoyed unchallenged authority by his people (compare Joshua 1,18) but died without leaving behind any children. Surely, this must have dimmed his joy on earth. If this was his lot, how much less joy can the righteous in our time expect to enjoy while on earth!
The High Priest Eli who did have sons had to experience the loss of the Holy Ark, the curse on his children who had disgraced him. When he died at a ripe old age the immediate cause of his death was the news that both his sons had been killed in battle (compare Samuel I 1,9; 1,10). If this happened to a righteous person such as the High Priest Eli, what sort of joy can there be in store in this world for the wicked?
Consider the fact that on this day, Elisheva, daughter of Aminadav experienced greater joy than any man or woman before her. She saw her husband begin his career as High Priest; Her brother-in-law, Moses, became king of Israel. Two of her sons became deputy High Priests. Her brother Nachshon became the first of the princes to be honoured with bringing the sacrifices by laymen. Even she did not long remain in such a blissful state of joy seeing that two of her sons, Nadav and Avihu, died on the very same day at the hands of G’d. Considering all these examples we need not be surprised at Solomon’s warning not to be frivolous, not to dance with joy, as such joy is apt to be all too brief.

And shall remain there forever. Forever in the Levitic sense,³³It can also refer to the fifty year period of Yoveil. i.e., fifty years as it is said, "from the age of fifty he shall retire from the work force."³⁴Bamidbar 8:25. Figuring as follows, we determine that Shmuel's lifetime was fifty-two years: Eili judged Yisroel for forty years.³⁵I Shmuel 4:18. On the day of Chana's prayer he was appointed judge.³⁶Above verse 9. By subtracting the year in which Chana conceived Shmuel, there remain thirty-nine years. Shmuel governed Yisroel from the time of Eili's death for thirteen years, as follows: On the day of Eili's death, the Ark was captured, and it remained in the land of the Philistines for seven months.³⁷Below 6:1. From there, it was brought to and remained in Kiryas Yearim until Dovid brought it up after he had reigned seven years in Chevron over Yehudah, and all of Yisroel had accepted him as their king. And it is written, "From the day the Ark came to rest in Kiryas Yearim, there ensued many days, and they became twenty years."³⁸I Shmuel 7:2. Subtracting from them seven years which Dovid reigned in Chevron discloses that from the time the Ark was captured until Shaul's death, were thirteen years and seven months; and Shmuel died four months before Shaul.

ותתכס AND [SHE] COVERED HERSELF — This has a passive meaning (she was covered); it is like (35:8) ותקבר “and she was buried”, and (1 Samuel 4:18) ותשבר “and [his neck] was broken”.