Looking at the Longman dictionary:
the (only) problem is (that) …
used before saying what the main difficulty in a situation is
Here is an example of a sentence starting with
THE + adjective + NOUN followed by the verb BE + a noun phrase complement:
We use a full stop to make sure our FOCUS structure is at the start of the sentence for iWeb:
. The _JJ thing|fact|point|problem|reason *
1 . THE ONLY THING I 20510
The only thing I can do is have you stay here until the check clears.
2 THE ONLY THING THAT 19898
The only thing that I do not like so much is that
I do not drive and I live far from everything,
so I have to use the public transportation to move around.
PELIC STUDENT EXAMPLE: Spanish Female level 4 grammar class.
3 . THE ONLY PROBLEM IS 10014
4 . THE GREAT THING ABOUT 7489 This is even more complex with the added prepositional phrase:
( about life on the street )
5 . THE IMPORTANT THING IS 6871
6 . THE BEST THING ABOUT 5459
7 . THE ONLY THING YOU 5054
8 . THE BEST THING TO 4209
9 . THE ONLY THING IS 3794
10 . THE ONLY PROBLEM I 3679
11 . THE GOOD THING IS 3658
12 . THE FUNNY THING IS 3436
13 . THE NICE THING ABOUT 3257
14 . THE WHOLE POINT OF 3206
15 . THE GOOD THING ABOUT 3085
16 . THE ONLY PROBLEM WITH 3060
17 . THE MAIN THING IS 2603
18 . THE ONLY THING WE 2552
19 . THE IMPORTANT THING TO 2437
20 . THE ONLY PROBLEM WAS 2366
21 . THE OTHER THING IS 2329
22 . THE WHOLE THING IS 2325
23 . THE BEST THING IS 2267
24 . THE BEST THING YOU 2243
25 . THE OTHER THING THAT 1818
26 . THE GREAT THING IS 1657
27 . THE ONLY THING TO 1560
28 . THE OTHER THING I 1543
29 . THE MAIN PROBLEM IS 1520
30 . THE ONLY THING MISSING 1449
31 . THE ONLY THING THEY 1425
PELIC B2 Student:
The only thing they want is to see that their children get the good education they have always wanted but couldn’t get.
Turkish, Male, level 4, writing class
32 . THE VERY FACT THAT 1359
The very fact that you‘re sitting here with us proves that it was preordained.
33 . THE SAD THING IS 1317
34 . THE REAL PROBLEM IS 1315
35 . THE WHOLE THING WAS 1273
36 . THE INTERESTING THING IS 1230
37 . THE MAIN PROBLEM WITH 1221
38 . THE BIGGEST PROBLEM IS 1219
39 . THE SIMPLE FACT IS 1144
40 . THE MAIN THING TO 1142
41 . THE COOL THING ABOUT 1106
42 . THE ONLY THING HE 1102
43 . THE ONLY THING LEFT 1051
44 . THE NICE THING IS 1022
45 . THE BIGGEST PROBLEM WITH 1015
46 . THE OTHER PROBLEM IS 978
47 . THE ONLY THING IT 968
48 . THE MERE FACT THAT 952
49 . THE WORST THING YOU 907
50 . THE ONLY THING THE 886
51 . THE INTERESTING THING ABOUT 880
52 . THE STRANGE THING IS 851
53 . THE OTHER THING TO 837
54 . THE WEIRD THING IS 828
55 . THE BEST THING I 788
56 . THE COOL THING IS 777
57 . THE MAIN THING THAT 764
58 . THE MAIN POINT IS 723
59 . THE MAIN THING I 723
60 . THE WHOLE POINT IS 717
61 . THE KEY POINT IS 690
62 . THE WORST THING IS 687
63 . THE MAIN POINT OF 676
64 . THE WORST THING THAT 674
65 . THE KEY THING IS 629
66 . THE BEST THING THAT 628
67 . THE IMPORTANT POINT IS 627
68 . THE BAD THING IS 614
69 . THE FOCAL POINT OF 585
70 . THE BEST THING FOR 544
71 . THE AMAZING THING IS 540
72 . THE KEY THING TO 540
73 . THE OTHER THING YOU 532
74 . THE BIG PROBLEM IS 518
75 . THE BIGGEST PROBLEM I 515
76 . THE ODD THING IS 506
77 . THE ONLY THING SHE 494
78 . THE ONLY PROBLEM THAT 486
79 . THE EASIEST THING TO 482
80 . THE FUNNY THING ABOUT 479
81 . THE ONLY PROBLEM ? 474
82 . THE BIGGEST THING IS 460
83 . THE CLOSEST THING TO 454
84 . THE WONDERFUL THING ABOUT 435
85 . THE WORST THING ABOUT 433
86 . THE CRAZY THING IS 421
87 . THE SAD FACT IS 409
88 . THE ONLY THING WORSE 405
89 . THE ONLY THING ABOUT 404
90 . THE IMPORTANT THING HERE 391
91 . THE BIGGEST THING I 386
92 . THE ONLY THING WAS 385
93 . THE SIMPLE FACT THAT 381
94 . THE ONLY PROBLEM WE 379
95 . THE AMAZING THING ABOUT 371
96 . THE BIG THING IS 358
97 . THE MAIN THING YOU 356
98 . THE ONLY THING WHICH 351
99 . THE ONLY THING BETTER 347
100 . THE ONLY THING THATS 346
1586, dm4, Chinese Fem, 3, w, 110 158,1,281
The final thing that contributed to my success was I practiced many times.
*The above example is repeated by many students with a different topic added in. There are hundreds of examples in the whole PELIC corpus where the structure is not so much about focus. Most function as complex transition signals.
206,gl6,Arabic,Male,116,4,w,27,1,205
The second thing that makes you a successful player is to practice these skills that I mention before in this paper.
572,az4,Arabic,Female,117,5,w,48,1,435
The last thing is that the student will benefit from this way of grading by knowing how to talk in front of others without difficulty.
3427,fl6,Arabic,Male,173,4,w,403,1,374
The one thing that kept him from doing that was that he thought about his future and how he’d be a success after he graduated.