"Once saved, always saved" is trite little quote that I can say I do believe, but am not completely convinced of it.
Unless God lied to me, when He promised "he who believes in the Son has eternal life", he actually meant "eternal life".
And did He actually mean "he who believes in.."? It's likely most or all of us know someone who says he/she "once believed," but no longer believes. So if that person truly does not believe now, are 3 possibilities then: (1)that person believed and had salvation and now does not believe and does not have salvation, (2)that person attained salvation and still has it in spite of having present unbelief, or (3)that person never believed. 'Customarily' a Baptist would say #3, but that may be a copout in order support a preconceived notion.
A few years ago I, too, might have said #3. But giving the matter a lot of thought, that is what I am not 'completely convinced' of now. Besides, if indeed there is no way to lose salvation once attained, then you cannot lose it by believing you can lose it. In that case, there is no reason to put a lot of emphasis on the doctrine.