I remember a conversation with my husband when Gwen was just a babe, about the daily daycare sheets. Every morning the person doing drop off (my husband 99% of the time) would fill out one side listing last diaper, last food/bottle/nursing, how they slept, and asking for any other important information. I noticed that he was writing basically the same thing every day. Now because we had a specific morning routine, the nursing time and diaper time really didn't change; but the "how they slept" part... well that changed drastically. But day after day, "fine." I questioned him about it, and he shrugged it off, asking what it mattered.
What I pointed out was this: Being a caregiver is like playing detective sometimes. Especially when you are watching a baby who isn't a great communicator yet, any clue that you can find which might help explain their actions is a huge help. Knowing that she had a horrible night sleep could be the difference between them recognizing her need for an earlier nap, or missing the window and ending up with a overtired mess of a girl on their hands. The same way that we learned from her sheets at the end of the day, that she might be extra hunger if she didn't eat a lot, or we might need to start bedtime a little early if she didn't nap well.
Gwen is four now, and there are no more daily logs of every bite, bathroom break, and certainly no more naps (::sigh::). But those little clues are just as important now. On evening that she's having a particularly hard time, its easy to just get frustrated, but its more productive to look for clues. Has she been sleeping well? Ask her about her day, did something happen? Its not always so cut and dry, but having some idea what might be causing the crankiness can make it a lot easier to handle, and be a bit help in figuring out what she needs to pull it together. Does she need sleep, or maybe just more hugs? Maybe she needs to be reassured that something that happened during the day isn't the end of the world.
As she gets older, there are more and more times when we can have real conversations about what is bothering her. But there are still times when I need to pull out my detective badge to figure it out.