Programmers frequently make observations, while deciding how to do something. Sidebrain provides a place to keep them handy.
To make an observation, use the command sidebrain-observe. You will be prompted for the text of the observation, which will then be displayed below your task stack, in the same emacs window. When ending a task which ends with a question mark, you will be prompted automatically for an observation. See Ending tasks for the actions taken on ending a task.