err 
/ˈeɚ, ˈɚ/ verb
errs; erred; err·ing /ˈeɚ, ˈɚ/ verb [no obj] formal : to make a mistake
▪ I may have erred in my calculations. ▪ The court erred in refusing to allow bail. ▪ To err is human. [=it is normal for people to make mistakes]
▪ I may have erred in my calculations. ▪ The court erred in refusing to allow bail. ▪ To err is human. [=it is normal for people to make mistakes]
err on the side of
◊To err on the side of something, such as caution, is to use or show more of it than may be needed so that you can be sure that you are using or showing enough of it.
▪ It's better to err on the side of generosity [=to be too generous] than to be too stingy. ▪ We chose to err on the side of caution [=to be very cautious] when planning our investments.
▪ It's better to err on the side of generosity [=to be too generous] than to be too stingy. ▪ We chose to err on the side of caution [=to be very cautious] when planning our investments.
