Your goal does have to be ambitious so your cause is worthy. Aiming at small things doesn’t make you excited or proud.
However, your goal still has to be achievable. If it is too hard, it will result in you getting frustrated and demotivated. Be realistic about what you set out to do. Consider your workload, availability, and commitments. If your goal is massive and you will need an hour or two every day to make it happen, is that realistic? I personally don’t know anyone who has that kind of time…
Equally, it is always a good idea to break a big, long-term goal into smaller, more achievable, short-term goals – into particular steps you will take towards your goal while making the big stuff happen. This will keep you motivated and you are more likely to keep going, feeling accomplished along the way.
E.g.: My big goal is to start thinking in English so that I can stop translating in my head and can answer faster, taking part in the conversation at a good speed, and feeling like the professional I am during our company meetings.