It's BECOME easy, but it wasn't always.
Especially being a SAHP, people often assume you have NO schedule, or that your schedule isn't "as important" as, say, someone at a paying job. Then, when I became a homeschooler, it became even worse. After a year of it I finally blew my top. After 2 years homeschooling I finally did a 'major gripe/rant' See this Q and the phenomenal response http://www.mamapedia.com/questions/17804342602795974657
A couple years ago was the WORST. We were new to homeschooling (after doing montessori preschool, and public K) and so called friends kept trying to use me as free babysitting. Or even paid babysitting. School breaks were actually ridiculous. Sorry, WE still have school. Or kiddo was at camp and that was/is my time to rock the 'self care', but others felt that "since I wasn't doing anything"... Nope. Huh-uh. Sorry!
If I take a day off THESE days, it's intentional. Just like someone taking a day off work (and I may be a stay at home homeschooling mom NOW, but I've worked paying jobs for more than half my life), I'll take a day or 3 off. For playdates (kid or adult), appointments, etc. But if I DIDN'T stand firm? I'd never get anything done. i'd get burned out, and stressed out, and behind.
Which I know, because I didn't always stick to my plans. And I do now. Which is heaven.