I've got a big DIY urge. My motivations usually include being too cheap to buy something (typically because I'm saving up for something else--right now, a 3D printer). A fair amount of the time there is vanity--wanting to brag online, say. Sometimes perhaps there is a minor motivation (which really should be much stronger) to repair things rather than wastefully throwing them out. And sometimes the activity itself is very pleasant (I really enjoy using power tools like a sewing machine, a drill press or a stand mixer; I like the smell of solder rosin or freshly cut softwood wafting in the air). But I think often the strongest motivation is the intrinsic pull of doing things myself.
According to Aquinas, that motivation is why Satan sinned. He wanted the good things that God was going to give to him, but he didn't want them from God--he wanted getting them himself. In other words, the first sin is Pelagianism.
This makes me a bit worried about my DIY urge. Is it an echo of the Satanic pride that led to the downfall of the universe?
Not necessarily. Aquinas' discussion of the first sin is driven by two theses: (a) Satan was very smart and (b) Satan's motivations were good. So Aquinas needs needs to identify a good motivation that led him to sin, not simply by a stupid mistake. It is thus central to Aquinas' story that the DIY urge that Satan had was a good motivation: there is a genuine good in achieving good things by oneself. But in order to achieve that good, Satan refused God's gift of grace, settling for (lesser, presumably) goods that he could get by himself.
The fundamental motivation behind the DIY urge is good, thus. But there is a serious danger that it misses what St. John Paul II called our "nuptial nature": that it is our nature to give ourselves to others and to receive others' gift of themselves. Satan refused God's gift. The parallel danger in the DIY case is that it not turn into a refusal of the gift of others' creativity and labor, a refusal to acknowledge that (to use older language) we are social animals.
Of course, the products of commerce are not gifts personally directed to us. (After all, we have to pay for them!) But there is a sense in which they still have some gift-like nature. People have chosen not to be subsistence farmers, but to make stuff for others. There is an imperfect duty somewhere around here to participate in the back-and-forth of commerce, which bears some relevant resemblance to the back-and-forth of gift giving and reciprocation. And so, like all things, the DIY urge needs moderation, not just for reasons like not wasting time or avoiding vanity, but lest it become a denial of our social nature.