 In one of Adorján 's books , GM <unk> Portisch opined that " at least two @-@ thirds of all ' tested ' openings give White an apparent advantage . " According to Portisch , for Black , " The root of the problem is that very few people know which are the openings where Black is really OK . Those who find these lines have nothing to fear , as Black is indeed OK , but only in those variations ! " Rowson considers this an important point , noting that " 1.d4 players struggle to get anywhere against main @-@ line <unk> and 1.e4 players find the <unk> and Sveshnikov <unk> particularly tough . " 
