No pain no gain
you have to do hard things in order to learn or progress
Going on a wild goose chase
Doing something that is pointless
Don't judge a book by its cover
Don't judge someone or something just by how they/it looks
Getting a second wind
Having energy again after being tired
Cutting corners
Not doing something properly to save time or money
Beating around the bush
To avoid sharing your true feelings because it uncomfortable
Letting the cat out of the bag
Saying something that was meant to be a secret
To cost an arm and a leg
It is very expensive
Giving someone the cold shoulder
Ignoring someone on purpose
On the ball
Doing a good job
Caught between a rock and a hard place
Having to make a choice between two unpleasant things
Once in a blue moon
Something that doesn't happen very often
Adding insult to injury
Making a bad situation even worse
Stealing someone's thunder
Taking credit for someone else's achievement
To bite off more than you can chew
Take on too much/agree to more than you are able to do
Beating a dead horse
Going on and on about something that is over and done with
Avoiding the elephant in the room
An issue or problem that someone is trying to avoid
Getting a taste of your own medicine
Being treated the way you treat others
Feeling under the weather
Feeling sick
At the drop of a hat
Right away
To give someone the benefit of the doubt
Believing someone's story even if it seems unbelievable
The last straw
The last thing to happen before something becomes overwhelming
Pulling someone's leg
Make a joke or teasing
Throwing caution to the wind
Being reckless or taking a risk
Bite your tongue
Don't say something out loud; keep it to yourself