Bonum facendum, malum evitandum is the axiom that governs our practical behavior: do good, avoid evil. What good and evil consist of is not always clear, but the axiom always holds.
Of the two, the malum is easier to define. The Ten Commandments list eight evils to avoid, but only two goods to do. Legal codes have all kinds of details about evil deeds, not good ones.
This is because evil is to be avoided absolutely. You have no moral right to do an evil deed, you are always obliged to avoid preforming one. But while doing good is morally obligatory in general, specific good deeds are not: you are obliged to do good deeds, but not (usually) obliged to do them in any particular way.
For example, it is always evil to steal. On the other hand while it might be good to give to the poor, what or how one gives is not a matter of obligation, but left to individual judgement and freedom.
A blogger I follow is considering becoming a vegan. Veganism can be, for some humans, a genuine act of virtue. But since humans are by nature predatory apes, veganism cannot be obligatory for them. It can be a specific good deed, and therefore a matter of individual freedom.
If we see veganism as an obligation it is because we see eating and exploiting animals as a moral evil rather than a material one, which explains why so many vegans seem stressed, guilty, and shrill: they are creating an obligation where there is only a potential act of virtue. Most vegans also give up on it after a while: the emotions motivating it are exhausting.
Sometimes a possible good deed appears on our moral horizon – perhaps an individual act or a long term project – and it resonates with something deep within us, and we think Yes! This is the good deed for me; I am the one here and now, I have the capacity, and I can give myself to this. There might be a feeling of fear or sense of sacrifice, but there is also a feeling of freedom and joy.
Other times we see a good deed and it feels like an imposition, creating a sense of anxiety and guilt. In this case, unless it is clearly a moral obligation (say, taking care of your aged parents or going to church on Sunday, to use examples from the Commandments) it is probably not the good deed for you.
When I was a teenager I was in a Catholic boys group, and one day we went to visit a seminary for a retreat. I remember meeting one young seminarian there who described his desire to be a priest as being based on the fact that the people God had planned for him to guide to heaven would go to hell if he were not a priest for their sake. Even as a kid I knew there was something fishy about that; today I would tell the young man, You are not called to be a priest. God is not holding souls hostage to extort you into Holy Orders. He can care for those people without your help, go home to your family. I can only imagine that feeling “the vocation” is more like the first experience of a potential good deed, not the second.