These three words all describe something you want to reach, but they are not identical. A goal is general; an objective is a clear, specific aim (common in study or work); a target is a specific number or result. You set a goal or target and later reach or achieve it.
Setting what you aim for
goal /ɡoʊl/ — Amina set a goal to read one article every week.
objective /əbˈdʒektɪv/ — Mei's objective was to improve her listening score.
target /ˈtɑrɡɪt/ — Diego set a target of twenty new words a week.
Not ""Diego made a target of twenty words."" — say ""Diego set a target of twenty words."". You set a target or goal, not "make" one.
Try it: Before the activity, Yasmin explained the specific lesson ___ so the class knew exactly what to focus on. (objective / growth / success) Answer: objective — An objective is a clear, specific aim, which is exactly what a lesson focuses on. Growth means development over time, and success is the good result at the end. Neither of those describes the precise aim you set before you start.
When effort pays off
These words describe reaching a good result. An achievement or accomplishment is a specific thing you did that took effort (countable, so you can have several). Success is more general and usually uncountable; you do not say "a success" for a personal result. Your attitude is the way you think and feel about something, and a positive attitude often leads to success.
achievement /əˈtʃiːvmənt/ — Finishing the course was a major achievement for Sofia.
accomplishment /əˈkʌmplɪʃmənt/ — Learning to speak confidently was a real accomplishment for Matilda.
success /səkˈses/ — Farid's success came from regular practice.
attitude /ˈætɪtuːd/ — Farid's positive attitude helped him through a hard week.
Try it: Wei listed all his ___ in his job application, including the projects he had completed. (accomplishments / objectives / challenges) Answer: accomplishments — Accomplishments are specific things you have completed through effort, which is perfect for a job application. Objectives are aims you still want to reach, and challenges are the difficulties you face, so neither fits a list of what you have already done.
Facing difficulty and getting better
A challenge is a difficult task that takes effort, and an obstacle is something that blocks your progress and has to be overcome. Growth is development or progress over time (usually uncountable, so no "a growth"). Improvement means becoming better, and it can be countable ("one improvement") or uncountable ("clear improvement").
challenge /ˈtʃælɪndʒ/ — Maya faced a challenge when she changed jobs.
obstacle /ˈɑbstəkəl/ — Losing her notes was an obstacle, but Maya kept going.
growth /ɡroʊθ/ — Amina noticed personal growth after joining the speaking group.
improvement /ɪmˈpruːvmənt/ — Mei showed clear improvement in pronunciation.
Not ""Amina noticed a growth after the course."" — say ""Amina noticed real growth after the course."". Growth is uncountable here, so do not use "a growth" for personal progress.
Try it: Changing jobs was difficult, but Maya saw it as a ___ that helped her grow. (challenge / improvement / success) Answer: challenge — A challenge is a difficult task that requires effort, which matches something hard that helps you grow. Improvement is the result of getting better, and success is the good outcome. The difficulty itself, however, is the challenge.
The mindset behind the effort
Motivation is the reason that keeps you working. Someone who is determined refuses to give up. Confidence is believing that you can actually do it.
motivation /ˌmoʊtɪˈveɪʃən/ — Her motivation comes from wanting to teach.
determined /dɪˈtɝmɪnd/ — Lars is determined to finish the course.
confidence /ˈkɑnfɪdəns/ — Speaking in public built her confidence.
Try it: Amina gets up an hour early to study because she badly wants to pass. Her ___ is strong. (motivation / obstacle / achievement) Answer: motivation — Motivation is the reason that makes someone keep working. An obstacle is something that gets in the way, and an achievement is the result after success, so neither one is the reason for starting.