“So teach us to number our days that we may get a heart of wisdom.” –ESV
“Teach us how short our lives really are so that we may be wise.” –NLT
“Oh! Teach us to live well!
Teach us to live wisely and well!”– MSG
Psalm 90:12, three different translations
Growing up we must learn different things.
We’re taught the alphabet, how to brush our teeth and use deodorant. We need to be educated, or tutored into many different skills. Our teachers direct and guide us, they provide for us an understanding of the skills we need to acquire. As we advance through their instruction, we grow in proficiency.
The Psalmist comes to the realization that he needs to develop a particular skill. He desperately wants to craft his life to be honorable and obedient. He turns to God and seeks His aid. The psalmist seeks a ‘teacher’ who will instruct him.
Our own lives are often chaotic and foolish.
We live in a great deal of ignorance, strained relationships and bad decisions. Most definitely we are ‘saved by faith,’ but the course of our lives can still be difficult. There is much to be learned in the spiritual world. We’ll make many mistakes.
The author of Psalm 90 doesn’t want to continue doing stupid things. He has a need, and he is pretty adamant that God will help him. Part of what he understands is that he needs to get ahold of the reality of the ‘shortness’ of his life. That’s a good start.
He must understand that he has a limited lifespan–an expiration date.
He refuses the deception that life will just always continue unfolding. He doesn’t buy it. He counts on God to pace him, and to keep him from recklessly wasting his life. He is asking for restraints. He must learn to say “no” and say “yes” to many things.
I encourage you to consciously make this step. Be deliberate in this. If we lack wisdom, we need to ask Him for it. Apart from His presence, our lives grow increasingly irrational. Living without restraints will lead us into more foolishness and despair. We must learn to say “no.”
“Making the best use of the time, because the days are evil.”
Ephesians 5:16, ESV
“The most important thing to remember about depression is this: you do not get the time back. It is not tacked on at the end of your life to make up for the disaster years. Whatever time is eaten by a depression is gone forever. The minutes that are ticking by as you experience the illness are minutes you will not know again.” 
Broken Believers 