For if your brother is grieved by what you eat, you are no longer walking in love. By what you eat, do not destroy the one for whom Christ died.
Romans 14:15 ESV

In the context of eating meat that could have been sacrificed to idols, what you eat could grieve your brother in 3 ways.

1. He could be disgusted by it, making fellowship difficult.
2. He could believe you are engaging in idolatry by eating meat that was dedicated to a false god.
3. He might take your liberty as permission to do something counter to his own conscience.

Pressuring someone to violate his own conscience could lead to him to committing an actual sin because he no longer trusts his own judgment. Overruling your own conscience in one case makes it that much easier to overrule it in the next, until you really are crossing the line into what God has forbidden.