Everything?

"I can do everything through Him who gives me strength." Phil 4:13

I suppose Paul was saying this in a particular context, but it seems that many people use this quote in different contexts. What exactly does Paul's statement mean? For example, today I prayed to God that He would help me be more diligent with my studies. I know I can be pretty lazy, but I really want to change this about myself. I know that God detests sluggards! And I told myself that I could do this, if only He would give me the strength. Of course, I know that if God wants to, He can give me the strength, but who is to say that He will? I suppose I need to keep praying.

Also, "Forgetting what is behind and straining toward what is ahead, I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus" Phil 3:13-14

Recently my mother told me that in order to reach my "goal," which is Jesus, I need to do two things: 1) Continually seek to know Him, 2) Fulfill my duty as a student and put all my energy and effort into my studies.
I've been really confused about this dichotomy-- Just everyday choices I have to make. For instance, if I had to choose between spending a few hours helping out a friend in great need, or studying for a test the day, what should I do? That's kind of a bad example, but... If you had to choose between doing your duty as a student for God, and "being Jesus" to someone, what would God want you to do? Am I thinking too far into it? Sometimes I feel like I'm trying to be too kind or too holy, at the expense of my own good, and at the expense of wisdom (I think I'm foolish). And yet, didn't Jesus call us to be like children, who love and believe without a selfish thought? Who is better in Jesus' eyes: the wise holy person or the rather foolish and naive child who, though without much reason and rationality, is able to love and serve others precisely because of his naivety?