Parents: What do you currently find to be your biggest struggle in parenthood?

My biggest struggle lately is teaching my preschooler patience when it comes to getting someones attention. She has had absolutely no patience lately. Scenario example: She says "Mom?" and I don't answer within two seconds (not exaggerating on the two seconds), so she says "MOM!" and keeps it up until I do pay attention. It's horrible when I'm busy or am in a conversation with someone else. I never really had this problem with my first, so I'm not sure what to do besides keep reminding her to be patient. It's not working too well so far.