Failing, again, again, and again...
For the experiment of searching for the Destructive Force carrier alone, Grimm had to face failure dozens of times every day. This was the "failed life" Grimm had been accustomed to, and he had gone through hundreds of years of that.
For the people who only saw Grimm's success and charm, how could they know how much effort Grimm had put in?
Loneliness, tiredness, hopeless depression and despair were like an enormous mountain standing in front of Grimm, but Grimm could only chop down the branches of the vast amount of trees on that said mountain, forcing himself to move forward little by little, and look for the dawn behind the extremely high mountain.
The process of going through endless failure to seek the truth, was all recorded in the Book of Truth that Grimm had accumulated day after day.
"Wah hoo hoo hoo! You lost my Enigma No.1! Give me back my Enigma No.1! I want my Enigma No.1 right now, boo hoo hoo!"