Maybe your friend said, “It’s HARD for ME to believe you.” He was using an adjective to show his attitude toward you (maybe he thinks that you are lying to him). This is modality using adjectives. The attitude of the English user can be given through a modality structure similar to: “It is ADJECTIVE for ‘someone’ to ‘do’…”
If your English is intermediate, you should understand this easily:
B1 point 100 in the category of Modality with adjectives in the English Grammar Profile is this structure:
IT IS + adjective + FOR + object + TO infinitive verb
The iWeb and NOW corpora do not allow for such a general search for
it is _j for _p to _v?i*
so here are the smaller results from the COCA corpus:
1 It is hard for me to imagine. 20
2 IT IS HARD FOR ME TO BELIEVE 19
3 IT IS HARD FOR ME TO SEE 17
4 IT IS BETTER FOR YOU TO ENTER 11
5 IT IS GOOD FOR US TO BE 11
6 IT IS IMPORTANT FOR ME TO GO 11
7 IT IS HARD FOR ME TO UNDERSTAND 10
8 IT IS IMPORTANT FOR YOU TO KNOW 9
9 IT IS DIFFICULT FOR ME TO IMAGINE 8
10 IT IS IMPORTANT FOR US TO UNDERSTAND 8
11 IT IS DIFFICULT FOR ME TO BELIEVE 7
12 IT IS DIFFICULT FOR ME TO SAY 7
13 IT IS DIFFICULT FOR ME TO SEE 7
14 IT IS IMPORTANT FOR US TO KNOW 6
15 IT IS IMPORTANT FOR US TO REALIZE 6
16 IT IS IMPORTANT FOR YOU TO UNDERSTAND 6
17 IT IS IMPOSSIBLE FOR ME TO BE 6
18 IT IS RIGHT FOR ME TO FEEL 6
19 IT IS DIFFICULT FOR ME TO ACCEPT 5
20 IT IS DIFFICULT FOR ME TO UNDERSTAND 5
With this narrowing down we can move to test: for the adjectives: “hard, better, good, important, difficult, right” and the infinitives “imagine, believe, see, enter, be, go, understand, know, say, realize, feel, accept” in the iWeb corpus:
It is hard… etc.
1 IT IS HARD FOR ME TO BELIEVE 167
2 IT IS HARD FOR ME TO IMAGINE 108
3 IT IS HARD FOR ME TO SEE 86
4 IT IS HARD FOR ME TO SAY 77
5 IT IS HARD FOR ME TO GET 75
6 IT IS HARD FOR ME TO FIND 69
7 IT IS HARD FOR ME TO UNDERSTAND 68
8 IT IS HARD FOR ME TO TELL 55
9 IT IS HARD FOR ME TO BE 44
10 IT IS HARD FOR US TO IMAGINE 42
better
1 IT IS BETTER FOR ME TO DIE 57
2 IT IS BETTER FOR YOU TO ENTER 44
3 IT IS BETTER FOR THEE TO ENTER 31
4 IT IS BETTER FOR THEM TO BE 28
5 IT IS BETTER FOR YOU TO BE 25
good
1 IT IS GOOD FOR US TO BE 89
2 IT IS GOOD FOR ME TO BE 27
3 IT IS GOOD FOR US TO HAVE 23
4 IT IS GOOD FOR ME TO DRAW 22
5 IT IS GOOD FOR YOU TO KNOW 18
important
1 IT IS IMPORTANT FOR YOU TO KNOW 555
(this is clearly the most common)
2 IT IS IMPORTANT FOR YOU TO UNDERSTAND 372
3 IT IS IMPORTANT FOR YOU TO BE 287
4 IT IS IMPORTANT FOR YOU TO HAVE 163
5 IT IS IMPORTANT FOR US TO BE 156
6 IT IS IMPORTANT FOR US TO KNOW 143
7 IT IS IMPORTANT FOR US TO UNDERSTAND 133
8 IT IS IMPORTANT FOR THEM TO BE 113
9 IT IS IMPORTANT FOR US TO HAVE 101
10 IT IS IMPORTANT FOR YOU TO GET 99
difficult
1 IT IS DIFFICULT FOR ME TO SEE 46
2 IT IS DIFFICULT FOR ME TO UNDERSTAND 45
3 IT IS DIFFICULT FOR ME TO SAY 43
4 IT IS DIFFICULT FOR ME TO FIND 32
5 IT IS DIFFICULT FOR ME TO IMAGINE 30
If you like this longer B1 grammar structure, also note that you can shorten the form by removing the adjective, and it is still B1 complexity: