פירוש על ברכות 68:15

HE SHOULD FOCUS HIS HEART ON ONE OF THEM. The Gemara said that if one cannot concentrate properly on the entire sh’moneh esray, he should at least concentrate on the first b’rochoh. It seems that one fulfills his obligation to pray even when concentrating on only the first b’rochoh. And that which we said at the end of perek T’filas Hashachar (30b), that a person must always assess his ability to concentrate, if he estimates that he can concentrate he should pray and if he estimates that he cannot concentrate he should not pray. On the surface it would seem from that Gemara that he must be able to concentrate for the entire prayer, since the Gemara speaks of his ability to pray, we should assume that it means an entire prayer and that concentration for one b’rochoh is not sufficient.
We can explain that there is no contradiction and the Gemara there as well means that he must assess whether he is capable of concentrating for one of the b’rochos.