How can I fix this "pen stroke"?

[dylanw14797408]

This "pen stroke" effect, for the lack of a better term, consistently appears whenever I use Illustrator. It doesn't look very clean, which is the look that I'm going for. I'm fairly new to Illustrator and I'm using Windows, if that changes anything. What I want my lines to look like are the other two lines that are seemingly perfect. Thank you in advance for your help!

p.s. sorry for large picture

[Monika Gause · Accepted solution]

Try View > Preview on CPU

[dylanw14797408]

Thank you.

[Jacob Bugge]

Dylan,

Ctrl/Cmd+E.

This toggles between GPU and CPU Preview, GPU causing the issue.

This is what GPU is about:

https://helpx.adobe.com/illustrator/kb/gpu-performance-preview-improvements.html