Or the weak person is easily stumbled or offended.
The cross reference takes us back to Romans 14.
(Romans 14:1-3) 14 Welcome the man having weaknesses in his faith, but do not pass judgment on differing opinions. 2 One man has faith to eat everything, but the man who is weak eats only vegetables. 3 Let the one eating not look down on the one not eating, and let the one not eating not judge the one eating,+ for God has welcomed him.
https://www.jw.org/finder?wtlocale=E&pub=nwtsty&srctype=wol&bible=45014001&srcid=share
Eating vegetables instead of meat also cross references with 1 Corinthians 8.
(1 Corinthians 8:13) 13 That is why if food makes my brother stumble, I will never again eat meat at all, so that I will not make my brother stumble.
https://www.jw.org/finder?wtlocale=E&pub=nwtsty&srctype=wol&bible=46008013&srcid=share
(1 Corinthians 10:23, 24) 23 All things are lawful, but not all things are advantageous. All things are lawful, but not all things build up. 24 Let each one keep seeking, not his own advantage, but that of the other person.+
https://www.jw.org/finder?wtlocale=E&pub=nwtsty&srctype=wol&bible=46010023&srcid=share
All things are lawful, but not necessarily advantageous. Paul had the right, the freedom to eat meat, but that might offend a brother or sister that is weaker in faith. Paul would choose to forego his rights and not eat meat if that meant not offending or stumbling one of weak faith. In this instance, it's not that the weak one insists on their rights, but that the weak one is shocked or offended by a certain conscience decision made by another Christian.
This principle applies to anything we may choose to do that might stumble or offend others. Substitute alcohol, or Disney movies, or nose rings in place of meat. Just because we can do something doesn't mean we should. Just because we have the right to drink alcohol, talk about Disney movies, or wear a nose ring doesn't mean we should if we know these things offend or stumble others.
Instead of insisting on our rights, we yield to the weaker Christian. We avoid these choices, not because they are wrong, but because we know they offend others.
For peace in the congregation, we give up our rights. To avoid stumbling a weaker person who simply cannot handle or accept a Christian would have a tattoo or wear a beard, or get our nose pierced, we choose not to do these things. We honor and respect those weaker ones by not causing undue offense.