Basically the part of the data set that failed the attention check is now considered just random noise. Which is something you want to minimize if you want to do any analyses or make any conclusions. You can analyze the others but again, youre just analyzing random noise.
I'm kinda afraid that I'm putting a selection for more conscienscious survey takers if I only select people who read the instructions, and this might influence the results.
The survey was pretty easy if you didn't read the instructions.