Having difficult conversations about poor performance should be conducted early before it impacts everyone else’s motivation to do good work. Poor performance from one person brings the whole team down. People will accept a new person learning, or a colleague learning new skills, and they’ll usually support someone through a very difficult time in their personal life (e.g., illness, or illness in their family), but they will not accept a poor performer on the team indefinitely.
There’s an old adage that by the time a leader is addressing poor performance, the rest of the team has been expecting it for a full year. If there is a poor performer on the team, you need to address it quickly.