The frustration felt by passengers when major engineering projects disrupt services poses a headache for the HS2 project, according to a watchdog.
How to rebuild London Euston station to accommodate the £55.7 billion high-speed rail line while ensuring services continue to run to an acceptable level is a "hell of a question", Transport Focus head of policy Mike Hewitson said.
He issued the warning after South Western Railway suffered the largest decline in passenger satisfaction of any operator in the past year - from 83% to 75%.
Almost 2,000 of its passengers were surveyed in autumn 2017, when delays and cancellations continued even after the £800 million revamp of London Waterloo station caused major disruption in August.
Southern, part of the Govia Thameslink Railway (GTR) franchise, suffered the largest year-on-year drop in satisfaction (down 12 percentage points to 65%) during the autumn 2016 survey.
That research was carried out amid the £7 billion Thameslink Programme, which contributed to poor performance along with driver shortages and industrial disputes.
Major construction work at London Euston will run from next year until 2033, causing significant changes to mainline services.
Mr Hewitson said: "The dilemma is how on earth you invest without things going badly wrong.
"The pain to get to the gain is really quite intense. How you manage expectations during that is going to be quite difficult.
"The scale of the disruption at Waterloo will be tiny in comparison with what's going on at Euston.
"How do you rebuild Euston station and all the stuff they need to do there without falling into what happened with Southern GTR and what's happening with South Western?
"I don't have any answer but it's a hell of a question."