In this day, a constant theme of Church leaders has been that of encouraging members to endure to the end.
In the days of the kings of Israel, this ability to endure required more than passive existence; it demanded great strength to prevail over all weaknesses. For example, a comment by the writer of Chronicles regarding Hezekiah seems to apply in almost a blanket fashion to the kings of Israel, from Saul and David onward." . . . God left him, to try him, that he might know all that was in his heart." (2 Chron. 32:31.)
Many times this testing came only after a strengthening experience, such as Asa being delivered from the Ethiopians (2 Chron. 14:9-12) or Jehoshaphat and his people being delivered from an aggressive host of Syrians. (2 Chron. 20:3-25.)
Ironically, the weaknesses in the hearts of kings were found not so much in war as in peace, and not so often in famine as in times of plenty; it was often later in life when the mighty fell from grace.
On the basis of Old Testament study, it might be suggested that generally a king's reign - and a man's or woman's life - extends long enough for each to seek the Lord and be strengthened, and, thus strengthened, for the heart to be fully tested.