Viktor E. Frankl said this quote

“ The pessimist resembles a man who observes with fear and sadness that his wall calendar, from which he daily tears a sheet, grows thinner with each passing day. On the other hand, the person who attacks the problems of life actively is like a man who removes each successive leaf from his calendar and files it neatly and carefully away with its predecessors, after first having jotted down a few diary notes on the back. He can reflect with pride and joy on all the richness set down in these notes, on all the life he has already lived to the fullest. What will it matter to him if he notices that he is growing old? Has he any reason to envy the young people whom he sees, or wax nostalgic over his own lost youth? What reasons has he to envy a young person? For the possibilities that a young person has, the future which is in store for him?No, thank you,' he will think. 'Instead of possibilities, I have realities in my past, not only the reality of work done and of love loved, but of sufferings bravely suffered. These sufferings are even the things of which I am most proud, although these are things which cannot inspire envy. ”