There are some aspirations I never try, because my Sims don't socialise. The outdoors aspiration is difficult, since you can't get beyond the first level without spending a good week in Granite Falls. The collector can be frustrating, because it seems as though the game spites you - you're getting crystals when you need frogs, or frogs when you need crystals. Usually, unless I'm playing a household dedicated to collecting stuff, I save those aspirations until they've already completed others and have more satisfaction points than they can use.
Some aspirations are long-range, so you have to switch back at the right times to complete them. The successful lineage would take an entire lifetime. Gardening is a bit more difficult with the new evolve schedule. However, I've noticed that you can cheat a bit (and this works for the collector aspiration, too) by moving items in and out of your Sims' inventories. (I generally don't do this on purpose, since I like the challenge of completing aspirations the hard way, but I've had it happen when I've transferred stuff for one reason or another.)