This is the 5724th most frequent Japanese word.
ついて行っ
"To follow" or "to go along with."
The phrase 'について行った' means 'followed him' and implies the act of physically following someone to reach a destination.
彼について行ったら、迷わず目的地に着いた。
Following him, we reached the destination without getting lost.
Here, 'について行く' is used figuratively, meaning 'to keep up with' or 'to keep pace with' abstract trends or changes.
時代の流れについて行くのは難しい。
Keeping up with the trends of the times is difficult.
The usage 'について行けない' implies an inability to physically keep up or match the pace of the activity described.