Significance of incorrect entry of Take off weight
I would further explain the remarks by Old Fella as I see it:
The significance of incorrect entry of take off weight is that there will be too much thrust reduction for the entire take off. This will result in the far runway fence appearing to get nearer faster than it will appear possible to rise above it, resulting in dramatic action by the sensible pilot at the last moment to avoid crashing through ground obstacles at the far end of the runway.