The time spent regretting yesterday, is only balanced by a longing to change tomorrow. Funny thing about life right now, is that it can seem only half fulfilled between what just happened and what will happen next. Why are you smiling? I fail to see the humor in that.
Assuming a gaussian distribution, there is a high likelihood that the real answer is in the middle – the joy of the “now” depends on where you set the variance of the before and after. I mean to say,
…it’s important to remain absolutely certain throughout your life…but one moment at a time.