There was a fad in the sixties "One Decision Stocks" -- buy them and never sell them. Ri-i-ght. No portfolio doesn't need to be tended and weeded. And you can't buy a basket that's immune either. Baskets do bust too -- a fund that's doing well for ten years might drop like lead in one more.
Being in for the long term doesn't mean always being fully invested or high-percentage invested in stocks, nor even holding beaten down stocks without a reason more than "well I bought it for the long term." Actaully I think that avoiding the hassle of selling and what goes with it, is a good and honest reason to hold -- far more honest than the "Well I bought in for the long term." That honest reason allows a alarm to be heard at some point at least, and the desire to rescue remaining value supasses the desire to avoid hassle. Harder to surmount the pyschological barrier that the motto "in it for the long term" throws up.