I have told my kids that one optimistic yet realistic way to look at life is that it is like standing in front of a conveyor belt upon which a stream of opportunities are passing by, but each one will never pass by again in the same form.
I am referring to every sort of opportunity: opportunities to make friends, to be kind, to find love, to have fun, to stand up for your beliefs, to show mercy, to develop interests, to develop good habits of character, to make money, to be forgiving, to practice strength, to find God, to learn, etc, etc.
Alas, that conveyor belt offers just as many opportunities to make mistakes and poor choices.
It is a tough part of maturity to accept the reality limitation, however, that any opportunity grabbed will reduce the number of opportunities passing by on the conveyor belt, because time is an arrow.
A friend reminds me of the old story:
The levee broke and the water is rising in the town. One guy gets on his knees and prays "God, save me from this flood." There is a knock at the door and a firetruck offering to evacuate him. "No thanks, God will rescue me." He waits as the water fills the first floor. A guy in a rowboat shows up. "No thanks, God will save me." Water fills the second floor and he goes to the attic and punches a hole in the roof. A helicopter comes by. "No thanks, God will rescue me." The water rises further, and he starts treading water, but finally tires and drowns. Up in Heaven he berates God. "Hey, you said you would help me when I was in need. Where the heck were you?"
God replies "I sent you a firetruck, a rowboat, and finally a helicopter. You rejected every one..."