I started going over to him and he stopped crying as soon as he saw I was getting up. My mom piped up, "See, he's manipulating you. He doesn't really need anything." I kept going, picked my son up, glared at her and said "He stopped because he knows I am going to fix whatever is wrong. He was fussing because that's how he communicates at this age. How else is he supposed to let me know?"
I was like, what if what he "needs" is that he's bored or lonely? What else is he supposed to do about that if not fuss? At 4 months old, it's not like he can ask mom nicely "Please pick me up" or walk over to the toybox and find something to do!