I climbed a huge Deodar his week, over 100 yrs old, historic property...I had to trim some lower branches for clearance...thankfully the owner said 'err on the side of more rather than less', she said it would be grown back in a bout two years!
I always have a 'moment' before working on old, established, cherished historic trees...a combination of: how lucky am I, a keen sense of responsibility to do the work properly, and a bit of oh shit, don't mess it up!