Your post shows a simple misunderstanding
Remember that signals ADD UP. So when two -6dB sources play at the same time, the master shows 0dB (6dB being 50%).
The best analogy for mixing is a tree (or river). All those little branches/tributaries are very little, meeting up to make bigger branches and so on, eventually all meeting in the trunk/river.
By definition, none of those branches can be bigger than the the trunk - it is nonsensical when you think about it.
So just remember to keep your branches in the right proportion, and (IMHO!) Keep the 'trunk' the same size by not moving the master fader if it clips. Learn to mix so that you don't need to move the master fader.
re: Bob's 32-bit point, ignore that for now. Bob's right in that 32-bit has bundles of headroom, but as soon as the signal hits the DA convertors (which make the 1's and 0's into sound), the 32-bit advantage is lost as all convertors these days are 24-bit. So the signal hits a 'bit depth bottleneck', and therefore WILL clip.
Bob's advice about starting with all your faders down a bit is VERY sound. Personally I prefer just to have the sounds made quieter before it even gets to the faders, as fader resolution is much finer near 0dB. In a perfect world all sounds are 'recorded' at the right volume, and you don't have to touch anything
Aim for that, your mixes will thank you!