1. Chance of getting a legendary is very low - like half a percent. 

2. Opening 10 at a time does not increase your chance of pulling a legendary.

3. You can increase the chance of pulling by pulling during 2x events.

4. Keep track of your mercy counter.

#4 is a recipe for sadness.....

I think pulling in general is a recipe for sadness 😂. I can count on one hand the legendaries I pulled within 100 shards of each other lol. More often than not, my pulls come very close to mercy before I get another lego, so I try to keep than in mind in case of Extra Legendary events. 

Pulled 105 shards, got nada, just 4 or 5 epics. Still these things happen. Moved onto my ftp account opened 6 epics bang 2 legos. Such is life. My mercy near full on my main, so will gather shards for next 2x event. Legos hard to get, so a pretty much solid 2 for 1 worth waiting for. 

This is an important lesson in life in general.  Always read the terms and conditions, and understand the situation that you are about to walk into.  The odds of getting a legendary is written in the portal at 0.5% for Ancient shards, which sounds like what you are pulling.  This means you have a 99.5% chance of not getting a legendary.

Fortunately this is just a game, but there are definitely situations that are much more severe in real life if you are not paying attention.  I think this has been valuable