I feel like that image is distracting from the point.
Nil is a value and also a symbol. (In some Lisps. Definitely in Common Lisp.)
Nil may be written as a symbol nil or it may be written as an empty list (). Same thing either way.
Nil evaluates to itself. In contrast, most symbols (but certainly not all) evaluate to their bound value. [I’m aware that statement is a simplification, gotta start somewhere.]
In any evaluation context, a symbol such as foo is evaluated. Quoting that symbol means evaluation “consumes” the quote and leaves just the symbol. So the evaluation of 'j is j, and so forth. Naturally the evaluation of 'nil is nil. But without evaluation, 'j differs from j and 'nil differs from nil.
I feel like that image is distracting from the point.
Nil is a value and also a symbol. (In some Lisps. Definitely in Common Lisp.)
Nil may be written as a symbol nil or it may be written as an empty list (). Same thing either way. Nil evaluates to itself. In contrast, most symbols (but certainly not all) evaluate to their bound value. [I’m aware that statement is a simplification, gotta start somewhere.]
In any evaluation context, a symbol such as foo is evaluated. Quoting that symbol means evaluation “consumes” the quote and leaves just the symbol. So the evaluation of 'j is j, and so forth. Naturally the evaluation of 'nil is nil. But without evaluation, 'j differs from j and 'nil differs from nil.