You're not paying attention. That's why.
Try blinking more often. It helps.
Or maybe just use your other eye.
Also, try adjusting your browser's contrast settings. Or your monitor's brightness settings. Or your therapist's settings. Just try everything, okay?
If none of these help, it's probably because you're not looking hard enough.
Or you might be blind. Just a thought.
Anyway, here are some links to help you see:
Or just Throwing Money at the problem.
That usually helps.