No. Saying “I will try” is not a sign of failure. It’s a sign that you aren’t full of arrogance. It’s a sign that you don’t completely lack self-awareness. It’s a sign that some tasks are difficult. It’s a sign that you’re aware that some circumstances are out of your control. It’s a sign that you’re human.
Not that I’d advise you to say “I’ll try, boss” when she tells you to get into office on time. But if she gives you a task that you haven’t done before, it’s okay to say “I’ll try.”
If you’ve never created a case study on your own before, it’s okay to say, “I’ll try.” It’s also okay to say “I’ll try to get this done tomorrow” when you need answers from Abhijeet the Account Manager and he’s been too busy to talk to you.