Run through each assumption (whilst the post it note is still on the canvas) and decide the likelihood of this assumption being proven wrong. i.e. you are looking for your weakest assumptions. Assumptions you have the least confidence in.

You can do this by use of the numbered stickers. Put a 1,2,3 sticker on each post it note. 3 is the assumptions you have least confidence in.

If you find people seem to have a difference of opinion on the scale, then spend a few moments to agree on the scale you'll use, that is relevant for your business. Try to do it so that you have a similar number of post it notes with a 1 or 2 or 3 on them. i.e. so that your scale is roughly balanced.