A Fragile Quine

Python 3, 45 bytes

c='print(end="c=%r;exec(c"%c+c[8*4])';exec(c)

Switching to Python 3 so that the trailing newline can be easily removed.

I started out with a stupid structure that had 2 variables instead of 1, but switching to 1 variable only made it 4 bytes shorter.

-(4 + 3) bytes by Dennis.

This was fun!

Now I know about assert:

s='s=%r;assert len(s)==34;print(s%%s)';assert len(s)==34;print(s%s)

If a char from string is removed, assert error. I would have done this sooner had I known of this feature, assert.

lambda s='lambda s=%r:s[22:]%%s%%s':s[22:]%s%s

Verify it on Ideone.