I learned a lot from this tutorial about gain:
https://www.youtube.com/watch?v=Iv5H59Ri9as
 

Wow, time to unlearn everything. IF I clip the source track causing audible distortion I can remove it during the mix??? I can't wrap my brain around that. Sounds like quantum theory, where things can be, and not be, at the same time. I'm having an Advil moment right now. 

Easy to understand video (IMHO):
 
https://www.youtube.com/watch?v=T-TpPLzRpsU

ampfixer
IF I clip the source track causing audible distortion I can remove it during the mix??? 

I know you're being silly, af, but somebody might read that and take you seriously. Nothing clips within the DAW. If you distorted it while recording, well, that happened before it became DAW data. So there.

No Dave, I'm not being silly. I honestly don't get it. It's obvious that my analogue brain is completely missing a fundamental bit of information. I REALLY don't understand the concept underlying you explanation. If it doesn't clip within the DAW, where does it clip? I'm feeling pretty stupid. 

ampfixer
If it doesn't clip within the DAW, where does it clip? I'm feeling pretty stupid. 

After this my study and after the collaborations in this topic, I understood, in summary, that the audio clipping occurs effectively in 2 moments:
1) In the last step of the last BUS, where the final audio file will be generated;
2) Or, eventually, within some VST placed on some intermediate track or bus, which does not know how to deal with excessive volume.

rogeriodec

ampfixer
If it doesn't clip within the DAW, where does it clip? I'm feeling pretty stupid. 

After this my study and after the collaborations in this topic, I understood, in summary, that the audio clipping occurs effectively in 2 moments:
1) In the last step of the last BUS, where the final audio file will be generated;
2) Or, eventually, within some VST placed on some intermediate track or bus, which does not know how to deal with excessive volume.

There is one other, less likely case: if a user has set the render bit depth to 24 or 16, any intermediate clip/track bounced or frozen could clip. The default is 32 bits, which behaves like all internal calculations, allowing large level changes without clipping, and with great dynamic range. The render bit depth is configurable in Edit > Preferences > File - Audio Data : File Bit Depth : Render Bit Depth.

I can't believe that I've completely missed a fundamental concept like this. Thanks to everyone for pointing me toward the truth. It's going to be tough. All the threads about tracking levels and I've never seen this mentioned. It was always track at -8 to -6, and leave room on the mixdown for mastering. 
I've been to professional studios where they watch the levels like hawks and never go near 0db. Must be residual thinking from the old days.
Thanks again for the education.

This doesn't mean you can ignore proper gain staging techniques!
 
Like Dave said, if you clip on the way in to Sonar you're stuck with it and no amount of mix wizardry will unclip it.
 
Once you have a healthy recording IN Sonar you can mangle it up all you want, (paying attention to gain staging throughout for clean, spacious mixes), but you can certainly overload tracks and easily compensate for this at either bus or master level, nothwithstanding the fact that certain plugins do not react well to having their inputs overloaded.

bitflipper
 
Here's the short answer. It's not 100% technically complete, but that's why it's a short answer.
 
Digital audio does not clip within the DAW, up to and including the master bus fader.
 
When a meter indicates clipping, it's predicting the future; no clipping has actually occurred yet but probably will happen once the data leaves the DAW.
 
So your intuition is correct: you can indeed turn the gain down at the master bus and erase any previous level sins. 
 
However, there is one big caveat. The data passes through many individual processors before it gets to the master bus, and you can't know with certainty that none of them will be thrown off by positive dB values. In fact, experience has taught me that many plugins don't handle it well. The result can be a subtle degradation that you might not even notice until you bring everything down and suddenly your mix sounds better. Sometimes, the degradation isn't subtle at all.
 
Bottom line: you're better off keeping levels under control at every stage.
 
 

This is a great explanation, but I'm still confused why in rogeriodec's example, when he boosts the signal by +6db, it actually shows clipping?  Is that because bouncing it sends it through the master bus and therefore makes it actually clipped in reality?