Unfortunately that is what the unit trust wants you to believe, but they are often FORCED to sell low buy high. Simple reasons but makes a world of difference. UT is not immune to market euphoria.
1. During good economic times, share market go up and up, lots of people dump money into UT (due to greed), hence the manager have lots of cash. With such large influx of cash, they have to maintain their minimum stock holdings (most around 85%). So? The manager is forced to buy more and more as the prices are climbing and people keep on dumping money into UT hoping for spectacular gains.
2. During poor economic times, stock market is crashing, all the poor investor panics (due to scared of losing money), so they withdraw lots of money from the UT. Usually a UT keeps about <5% of it holding in cash, so if there is a large redemption from the investors, what can the UT manager do? They end up having to sell shares near it's lowest point to raise cash to pay off all the panicking investors.
3. Most UT are hampered by lots of holding rules, which actually handicaps the manager. For example most stock UT must hold a minimum of 80% in publicly traded stocks. In poor times which the market falls, the manager even however brilliant he is, he cannot sell off all his holdings to bond or cash.

Thanks Gark. Your information is a real eye opener. I am now a more informed UT buyer. Thanks!