When sitting down at a Blackjack table, how bad should you be doing before deciding to walk away. After losing the first 3/4/5 hands in a row? If I sit down at a $25 table with $500 in my capital, how should I decide when to walk away before losing all of my money. In other words, how quickly in terms of time and money, should I decide that the deck is not on my side and I should try another table.

I like to go to a casino with $2,000 and where I like to go the lowest table min is $25. This means that I would optimally bring $500 to said table for adequate capital. That being said, if I were to spend all of the 500 and lose at 4 tables, my bank roll would be gone. So I'd like to keep myself from getting slaughtered if possible.

It's difficult because I once sat down at a $50 dollar table with $500 bankroll, and with my last 50 bucks I ended up walking away with $5,000. But more often than not, when you've lost half your money and you feel like you're going to lose the rest of it, you do.

I'm also looking for opinions on these matters:
1) Fact or myth: Is it just me, or is it VERY difficult to get in a good win streak in double deck tables
2) Fact or myth: In my limited experience, I've had much much more success on higher limit tables with fewer players (pref heads up). Now I know about the concept that playing heads up means the dealer gets 50% of the BJ's, but can having several people at the table dilute the cards so much that it's hard for you to win consistently?

PS. I do not count cards (not much knowledge of it, I'm only 22 so I haven't been playing long but I would like to be as experienced as possible without cheating)

I follow a simple progressive betting method that minimizes losing streak damage and maximizes those lucky long winning streaks.
I've already had enough bad experience with regressive bets, like the time I took $100 to $900 on roulette, just to lose it all in a matter of minutes.

Thanks for any info guys.