Why is it so much easier to cut acquaintances slack than those we love the most? Is it that we don't have to deal with them as often, making their flaws less noticeable? Or is it simply that we don't care for them as much? A fault (even a rather pronounced one) in a casual friend isn't as concerning to us because we aren't as invested in them in the same way that we in our family. Maybe we feel no responsibility for them... it's their life, who are we to interfere? Our parents, siblings, spouses and children on the other hand, are a completely different story. Not only do we want them to be as perfect as possible, we have had much time to acquaint ourselves with their every blemish. We feel our relationship gives us the right, nay, the responsibility to intervene on their behalf and save them from themselves.
I find myself repeating "It is not my job to fix them." The only one who can seems to take His time, and works on me in the process.