Time and energy to revise your work accordingly.
It takes time to find the right agent for your work, too. Scoping them out online and reading about the types of work they're looking for becomes a seriously consuming thing. I wouldn't want to bother someone with something they're truly not interested in. There are agents who use their positions to broadcast their politics loudly on social media, too. I'm not too sure how I feel about that. Artists do it too. I'll follow them to see more of their work, and 3/4 of their posts are about refugees, racism, and riots. You have a platform to share your soul, and you chose to post links to mainstream news? Alright.
Making the product is only a portion of the work. There are rejection letters. Oh man, are there ever rejection letters. And that's alright. It just means the agents don't know how to market what I've made, or they aren't advocating my ideas. (Or possibly my editor and I missed an embarrassing, mood breaking typo.)
Wish me luck. I can't turn back now.
PS: The art I'm working on right now uses this interesting design from a hotel in Chicago that I visited circa 2011. The ceiling fans at my grandmother's home have a similar pattern.