Little brother writes motivational notes for sister crying in the bathroom and she shares them online.

When at their most evil, siblings can push all your buttons, narc on you to your parents, and reveal your most embarrassing moments to anyone who will listen. They can function as living, breathing manifestations of every pet peeve you've had, and they'll fully do it on purpose to get a rise out of you.

However, when their shadow side dissipates, siblings can also be some of the most ride-or-die friends imaginable. They already have an acute understanding of the cross you've had to bear growing up, so when their powers are used for good, it can be a blessing.

The Twitter user AnnieDaGrannie recently experienced the sweeter side of her 10-year-old brother during a crying spell in the bathroom, and shared the anecdote with her followers.