That's why I suggested not bothering, just use the best rate things like everyone else. But if there was a big difference between what a "safe" fund would get you and a bldg soc, then it would be worth learning a little.
It's perfectly possible to use types of Bond, and approaches, where your drop would only be tiny and a small fraction of what you'd gained.
This was one: the grey trace one being the whole stockmarket (S&P500) and the upper blue one a managed bond, with Building society returns the low two:
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Harder now that interest rates have dropped, See how the top one has gone pretty flat. But rates may notch up again so - keep asking.
That's about 6% compounded, which isn't bad.
A I these days is good for wondering about what-ifs. You can ask it what happens if you do xyz.
Then you could spit your investment perhaps.
If you'd got up to +70% you wouldn't be bothered by that little wiggle.
There are also DIvidend options you can use.
If your money's in a SIPP it's a way to get some money out, tax free
eg in 12 months to date:
HSBC has produced 4% dividends, while the stock itself went up 75%
Aviva (insurers) paid out 6.25%, while going up 25%.
These aren't fly-by-night companies, so you can see the attraction.
Even if the stock itself does dip, you still get the dividend.
It's not hard to find those.