Joe Schmidt says he is "scared" at the thought he could become only the third coach to lead Ireland to a grand slam if they beat England in their final match in the Six Nations on Saturday.
The 52-year-old New Zealander, who secured his third Six Nations title in the past five years last week with a game to spare, admitted his players would need to reach new levels of excellence to complete a clean sweep.
Apart from the three titles under Schmidt, who took over a demoralised squad after the 2013 Six Nations, the Irish have recorded their first-ever victory over world champions New Zealand, a record home win against South Africa and are on a record national winning run of 11 Tests going into the England game.
England may have lost their past two matches and seen their hopes of a third successive Six Nations title dashed but they are unbeaten at Twickenham since Eddie Jones took the reins following the 2015 World Cup debacle and would love to do to the Irish what they did to them in Dublin last year - deny England a perfect season.
"I'd be more motivated and scared by that than thinking about how fantastic it would be to do something that would be another step for this group into kind of stretching themselves beyond what they've done before," said Schmidt, referring to the Irish teams who swept the board in 1948 and 2009.
Schmidt, who is likely to bring the curtain down on his tenure after the 2019 World Cup in Japan and return to New Zealand, said while he is a "glass-half-full person", he is not immune to thinking about how the dream might turn into a nightmare.
"I wouldn't say that you can control that emotional rollercoaster that preparing a high-level sports team kind of engenders," said Schmidt.
"Because there are times where you inevitably imagine the worst-case scenario. Worst-case scenario is that England hit the ground running and they actually win with a bit to spare
"It would be a crushing way for us to finish a year of being unbeaten."