I can relate to this pattern in my own life, can you? We start Monday out with good intentions to exercise, but by Wednesday inspiration is needed to get through the rest of the week!
What's interesting to note is that these topics by day don't correspond to Twitter hashtags. For instance, #MeatlessMonday is usually about healthy eating on Monday, but the most pins for food fall on Sunday according to this data.
It's important to know your social media platforms. What works on one, may not work on another.