I started investing in stocks in 2010

[NesuD]

Perhaps thats true. But I didnt time anything.
I bought the funds when a very expensive and supposedly competent financial advisory told me to get into them.
The stocks within the Mutual Fund were diverse.
There were no fees.

It just tanked.
And I lost money. Like, most of it.

Based on the time frame I'm guessing you got burned by the Dotcom Bubble. Everyone did. That was my first major learning moment. I lost over 60% of my investments in that. I did not bail from the market though. I became more educated about properly balancing my portfolio. I didn't run from the market like many did I kept investing new money and reinvesting what remained of my old money with a plan. Didn't have a plan until that happened. Diversification means far more than just having several different stocks or index funds. You want to be diversified by region, industry, and instruments. Targeting many different indexes that historically perform in a manner you are comfortable with is the best hedge for weathering downturns and capitalizing on bull markets. No matter how gloomy the markets are there is always sunshine in some market, region, or industry somewhere. You want to have some money in that sunshine.

 

[dullard]

Perhaps thats true. But I didnt time anything.
I bought the funds when a very expensive and supposedly competent financial advisory told me to get into them.
The stocks within the Mutual Fund were diverse.
There were no fees.

It just tanked.
And I lost money. Like, most of it.

Sorry that you lost so much. The bold underlined points don't compute. Also, no one is really that competent -- see Warren Buffet's bet that a simple index will beat professionally selected hedge funds. Hint: Warren is winning that bet.
http://fortune.com/2017/02/25/warren-buffett-scorches-the-hedge-funds/

 

[Sonikku]

...and I've been told since 2013 that the stock market is about to crash and that I should sell. I know it will crash sooner or later, but why do people still believe that they can predict exactly when it will crash? I'm invested in index funds only, btw. I know there was a minor crash in 2014 I think (I don't even check anymore), but it surprises me that people still think they can predict the stock market.

I think some people saw the 2008 crash coming a couple months before it happened.

 

[DaveSimmons]

I think some people saw the 2008 crash coming a couple months before it happened.

And some expected it earlier, and some expected it later.

If you have 100 people guessing about an event, some of them are going to guess right. The problem is you don't know which ones until it's too late.

 

[s0me0nesmind1]

Stupid question time: Why exactly do people use the term "compounding interest" when referring to investments? Unless your stocks pay dividends what is compounding?

A gain without a dividend is simply a gain.

 

[s0me0nesmind1]

I think some people saw the 2008 crash coming a couple months before it happened.

Which is actually a fact. A few people saw it coming and made big money betting against the real estate market.

The movie "The Big Short" is pretty damn good for explaining a lot in an entertaining way

 

[DaveSimmons]

Stupid question time: Why exactly do people use the term "compounding interest" when referring to investments? Unless your stocks pay dividends what is compounding?

A gain without a dividend is simply a gain.

S&P 500 dividend yield averaged 1.99% between 2009 and 2015.: http://www.investopedia.com/articles/markets/071616/history-sp-500-dividend-yield.asp

Mutual funds can be set up to automatically reinvest distributions, or with ETFs you can do it manually. Both generally do pay out something.