There are three types of decisions we make in life.
1. Trivial decisions, like what I decided to wear to the gym this morning.
2. Right-wrong decisions. Should I hide my income from the IRS or have an affair? I don't even need to ask these questions. The answers are already crystal clear. The Bible says I should not steal and I should not commit adultery. These matters are settled.
3. Wise-unwise decisions. Who should I marry? What career path should I choose? Should we homeschool or not? For these decisions, the Bible doesn't give me a clear answer. It requires discernment.
Now let's look at Phil. 1:10. Although the Greek here is a bit ambiguous, Paul's probably referring to the ability to make the best choices possible and to distinguish the good from the best. Later on in the chapter he will explicate exactly what this looks like. But for now, he's already established that the truly essential thing in life is gospel partnership (1:5). For Paul, this meant the Philippians' continued participation with him in gospel ministry. They alone of all the churches had established a partnership with him. This means, among other things, that they will strive for a unity of spirit in which powerful tensions are held together by an overmastering loyalty to each other as brothers and sisters in Christ. Such unity is only possible when Christians are humble and take gospel participation more seriously than their own self-importance. This point is clearly developed in the "heart" of the letter (1:27-2:11), where Paul shows that gospel partnership cannot coexist with individualism or partisanship.
Thus humility becomes, in Paul's thinking, the linchpin that guarantees the success of the partnership as self is subdued in the service of others. More on this when we get to Phil. 2:1-4.