Why do I feel guilty for being frustrated with my kids?

My 9yo and 7yo were fighting about a toy for literally 20 minutes this morning and I genuinely lost patience. Sent them to their rooms. Now I feel guilty all day like I'm a bad dad because I got frustrated. But like... I'm human? Parents are allowed to get frustrated, right? Or am I supposed to stay zen and understanding forever? This guilt spiral is worse than the frustration sometimes.