Why won't my sim sit still?

One of the features added in the sims4 was allowing sims to multitask, doing several things at the same time. The idea behind it was to save players time by having sims fill their needs at the same time. But that hasn't been well regulated, resulting in your sim possibly taking their plate of food to their nearest toilet and sit down to do their bladder business while continuing to fill their hunger need. And if you have another sim on the lot with high enough social relations they may walk in on your sim, be totally comfortable with what that sim is doing on the toilet, and start a conversation so their social needs also get filled...
Sims in the Sims 4 are very bad at focusing on just one task, especially with autonomy turned on, as the game will always look for anything else that sim can do in addition to whatever they're already doing and direct them to do so.