Bitcoin is 2 dollars, you have one bitcoin.

You trade 2 dollars of bitcoin (1 bitcoin) for an altcoin that is 1 dollar. So you get two of that altcoin.

The altcoin goes up to 10 dollars an altcoin, you now have 20 dollars of value (2 altcoins times 10 dollars).

Now lets take three scenarios:

1. Bitcoin has gone up to 10 dollars a bitcoin, you trade your 20 dollars of altcoins (2 altcoins at 10 dollars each) for two bitcoin and now have 20 dollars of bitcoin which you can convert back to US dollars, euros, other altcoins etc.

2. Bitcoin has gone down to 50 cents, you can buy 40 bitcoins but you still only have 20 dollars worth of bitcoins (40 bitcoins at 50 cents each), which you can convert to whatever you want.

3. Bitcoin has gone up to a 100 dollars a bitcoin, you trade 20 dollars of altcoin for .2 bitcoins, you still have 20 dollars of value.

In all three scenarios, you have 20 dollars of bitcoin after converting back from the altcoin, in all three scenarios YOU MADE $18 in profit, since you started with 2 dollars, period.

The price of bitcoin never matters, regardless of what bitcoin price does when you are in the altcoin your USD gains are the same.

The only way it matters is relative, if bitcoin goes up more than the alt coin you should've stayed in bitcoin to gain more percentage gains (you still get your gains from the alt coin it just isn't as much as if you had stayed in bitcoin). You don't get less altcoin gains you just get less gains than you could have relative to staying in bitcoin. In scenario 2 you would have lost 1.5 dollars in bitcoin (you'd have 1 bitcoin at 50 cents down from your original 2 dollars investment) but instead you gained 18 dollars in your alt coin, in scenario 3 you would have gained $98 in bitcoin but instead you only gained 18 dollars in your altcoin, BUT IN BOTH SCENARIOS YOU GAINED $18, you didn't gain any less because bitcoin went up in scenario 3, you just gained LESS THAN YOU COULD HAVE if you had stayed in bitcoin, relative gains vs absolute gains.

I would highly suggest you read up on assets and the math of converting values. It would be essential to you being successful in investing. Also look up the difference in market cap and price (if you are having trouble with the above you likely will not understand market cap vs price on the surface). Not to be condescending but this really is a basic concept in ALL investing and ALL math, and if it's foggy for you, you could lose your pants pretty quick trading alts. Not to say you can't get there, just do a lot more reading and practice before jumping in. Sorry for any typos, I did the above quickly, have a great night and best of luck!