First of all, we should understand the concept of "negative bending moment". The concept of bending moment was first learned from the "theoretical mechanics" of the university. The bending moment represents a kind of rotation. The physical (mechanical) meaning of the moment symbol is the rotation direction of the moment.

With the above concept, combined with the knowledge of structural mechanics, we know that "negative bending moment" refers to the rotation of a structure (usually a bar) with the upper part pulled and the lower part pressed. Also, the most common situation is that the bending moment at the bearing is generally negative, which is what we usually call "negative bending moment at the bearing".

Therefore, when we compare the negative bending moment, we only need to look at its size, not the symbol, because the symbol only represents the direction of the bending moment.

Finally, in physics and mechanics, many quantities have symbols, which represent different physical meanings. Some symbols participate in size comparison, while others do not (such as bending moment).