From Adam’s Ordeal (#28)
Q: How can one keep the idealistic teenage years always a part of him?
A: It depends what he was in those years. For a great many people, it pays to forget about their teenage years as fast as possible. But even if you had teenage years like Reb Yisrael Salanter, you have to know, the way to keep those years with you is to be true to yourself.
For a great many people, it pays to forget about their teenage years as fast as possible.
A man has to be true to himself. Always look back and say, “Can I disappoint this idealistic youth that I was? If he knew how I would turn out, would he be satisfied with me?” So always look back and be a neeman (faithful) to the self of your youth.
When I was in yeshiva, say, I wanted to become a gadol batorah. Now I was married and I fell into the maelstrom of life, and now years have passed by, I’m overwhelmed.., No! I can’t let that youth down. I’m going to go back to what I was once. I was sitting in a beis hamedrash dreaming dreams of greatness, I must come back again. You can do it, you can do it. Even if you’re well on in years, if you start with a systematic program. You're going to accomplish great things in your later years.
If you have that incentive of not wanting to embarrass your youthful ideals, “ashrei zikneseinu shelo bisha es yalduseiheim” (based on Sukkah 53a): Happy would be our old age if we don’t disappoint our youthful ideal. (That’s not exactly the phraseology there; I’m using it in my own words.)