system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 , How do windsurfers get back to where they started if the wind is only blowing one way?

The only way I can think that this would be possible is if the wind was blowing directly onshore?

Edit: thanks for all the well thought out replies. I think I’ve got it figured out know,  I’ve always Been a bit confused about ships tacking into to wind and I think the key thing I was missing was the sail being using like as an airfoil creating pull, used in tandem with with the fins/keel .
gpt
Sailing ships, and windsurfers, can make progress upwind by tacking. 

Say the wind is coming from the north. The ship can sail as close to the wind as northeast or northwest. So if it alternates, first going this way and then that, the *net* movement will be north.