Killing my friends

so i feel like d&d is fun but i want it to be a challenge for my friends not just a "Well we know we are going to win" kind of thing. i want to threaten them somehow so they think that they could die.

the other thing is, if they do die, well its kind of sad because i want them to be "the almighty heros" so i want them to stay alive.

agreed, the focus needs to be on "consequence for failure". in a purely combat oriented dungeon crawl, failure is usually dying. In a more intricate plot, you can have all manner of consequences which make them feel like their efforts failed - villages being raided or destroyed, kings being assassinated, undead armies rising, NPC's dying, party members getting cursed - have a think about what they care for (other than surviving) and make that the cost for failure.

thanks for the replies on this topic I never really thought about some of that. I think it will really help me in d&d ( ͡° ͜ʖ ͡°)