Sometimes you might find yourself debugging when you don't have symbols for a managed library - that is, you don't have the PDB file for it. In managed code, there is a whole lot of metadata lying around, so you can still set a breakpoint from Visual Studio. You won't be able to set it by clicking on the "left lane" even if you have the source file, because the debugger can't tell the association between running code and the file without the PDB file.
However, you can still go ahead and type the class/method name to set a breakpoint, just like explained on this How To. IntelliSense might complain that it cannot find the method (which makes sense), but if you go ahead and you typed correctly you'll see that you get a breakpoint with a full red circle. If you instead get a hollow red circle with a warning sign, that means that the breakpoint wasn't set; you can then mouse over the icon to get additional information about why.
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