A good friend (Avodah Zarah 15b)

When are you allowed to tell a friend not to do something and when should you keep your mouth shut?

Here's an example. If your best friend is overweight and goes on a diet are you allowed to remind them of this when they eat a giant burger? What if they don't go on a diet but you are worried about their weight?

This question is at the heart of today's daf. Here is the example we find today. Quoting from Mishnah Sheviit 5:6 we learn:

These are the tools that a person is not allowed to sell during the seventh year (the shmitah year when all land must lie fallow): The plow and all its accessories, the yoke, the shovel, and the hoe.

All of these tools are used to tend to the earth. We worry that someone who is known to violate the laws of shimatah wants these tools and therefore, we must not give them to him because we will be aiding him in sinning (working land that should be fallow).

The reason why we must not give him the tools is because we would be violating the prohibition from Lev 19 "Do not put a stumbling block before the blind." Our tradition teaches that all who sin are blind. We can think of it like they don't see the "light" of Torah. If we do anything to help them sin further (like selling them a plow) we are essentially puting a stumbling block before them.

To return to our question: are we allowed to say anything to our friend? I would guess so. We are reminded to rebuke our fellow in the same section of Torah as the precept not to put a stumbling block in front the the blind. And a person's health is a worthy cause to take up. However, our tradition is unequivocal that we must not serve our overweight friend a huge hamburger. That would be wrong and like putting a stumbling block before the blind.

(A note: Blind is sometimes an apt term for my eating. I eat mindlessly and often will sit down to eat a meal only to learn a few minutes later that I have eaten it without either tasting it or enjoying it).