Not taking it the wrong way, I'm more than happy to discuss.
I've been speaking to the Canadian version of MFS IV, but here's a link to the USD version (so the numbers are different) which has been around since 1995 but has the same mandate and PM. On the chart, stretch it to "maximum" and look at the performance against the index since 1995.
http://www.morningstar.com/funds/xnas/mgiax/quote.html
I could get into a huge story on MFS and it's mandates and how it picks its portfolio managers and all the due diligence they do, but it would likely be too long for you to care/read haha. Long story short, it's a company that was founded in 1924 and credited with the first ever open-ended mutual fund. You know what the first company they bought was? A little company called the American Telephone and Telegraph Company, better known today as AT&T. They have held that company for 90 years. They've been through the great depression, two World Wars and every market crash you can think of, and they're still standing. How's that for longevity?
The run doesn't necessarily need to "be over". You shouldn't have to know when to change funds, thats what an advisor is for. Advisors talk to ******** like me who say "Hey, you've been using Fund XYZ for the past ten years, well look at how much more money you could have made for your clients if you had been with us!" and they say "oh well **** me, I'm going to start selling this product to my clients instead!". They're the ones with all the info, you don't have time to siphon through 600 International Equity Funds to figure out which is best for you.
In terms of differentiation from picking a good stock/ETF, I kind of have to take two directions.
Stocks: Well, picking a good manager basically gets you 100 stocks. Do you have time to get to know 30+ holdings (in traditional finance, this is the level where diversification stops mattering) to diversify your portfolio?
ETFs: Again, ETF's are passively managed, so while it isn't different than picking a good manager, the benefit is much greater because a manager can be opportunistic when deploying cash. ETF's don't.
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Passive management aims to mirror an index. Any allocation changes are done to fulfill that objective, not to take any sort of conviction on a company, sector or country.